In boost converters, short-circuit protection is required to prevent the components from being damaged when a short-circuit event occurs at the output terminal of the boost converter.
In a prior art short-circuit protection method, a short-circuit protection (SCP) switch is coupled between a switching circuit of the boost converter and an input voltage and is disconnected to protect the boost converter when the output short-circuit is detected.
An external SCP switch is often used in prior arts to save cost and to improve electrical performances of the boost converter. Since the threshold voltage of the external SCP is uncertain, in the design of an IC controller for a boost converter, a design margin of a voltage provided to a control terminal of the external SCP switch is often required so that the IC controller can turn on most kinds of external switches.
In the above prior art short-circuit protection method, the output short-circuit is detected at the end of a predetermined fixed time period which begins from the moment when the boost converter starts up. However, the above method may be not accurate or prompt as the threshold voltage varies for different external SCP switches. FIG. 1 illustrates a timing diagram showing the operation of the prior art short-circuit protection method. In FIG. 1, t1 represents the moment when the boost converter starts up, t2 represents the moment when the external SCP switch is turned on, and t3 represents the moment when the short-circuit detection is performed, T1 represents the time period between the moments t1 and t2, T2 represents the time period between the moments t2 and t3, and T3 represents the time period between the moments t1 and t3. According to the description above, the time period T3 is predetermined and fixed and t2 is partly determined by the threshold voltage of the external SCP switch in the prior art method. Thus, if the threshold voltage of the external SCP switch is relatively large, the time period T1 will be relatively long and the time period T2 will be relatively short. As a result, an output capacitor of the switching circuit may not be fully charged at t3 and the short-circuit detection may be inaccurate. In opposite, if the threshold voltage of the external SCP switch is relatively small, the time period T1 will be relatively short and the time period T2 will be relatively long. As a result, the output short-circuit event may have occurred for a long time and the components in the switching circuit may have already been damaged. Thus, the short-circuit detection is not prompt.